100 Mr. H. J. Carter on a new Species o/'Tethya. 



longer and more inclined towards the base, where they are 

 continuous with those of the conical expansion, thus giving 

 the whole of the outer surface a white, glistening, asbestine 

 appearance. Conical expansion (fig. l,b b) smooth, even, 

 thinning towards the circumference, composed of long spicules 

 overlapping each other in parallel bundles, which, radiating 

 from a common centre at the summit, in continuation with 

 the lowermost structure of the head, become more or less 

 mixed with sand downwards {fig.l,d), and at length end 

 freely at the circumference in a circular, fringed border (fig. l,c 

 and fig. 3). Pores chiefly confined to the upper part of the 

 head (fig. 2, a) ; vents occupying the larger polygonal inter- 

 spaces at the base (fig. 2, 5). Vault or inner summit of the 

 conical expansion apparently occupied by a few pores and 

 vents, from which point the bundles of long spicules radiate 

 in all directions, to end in the fringed border just mentioned ; 

 more or less concealed in their course by a zonular layer of 

 sand, which covers two-fifths of the distance between the 

 fringe and the summit (fig. l,d). Spicules of the body, and 

 conical expansion probably, radiating in bundles from a com- 

 mon point or denser portion of the internal structure, called 

 the nucleus, to the periphery generally; held together by 

 sarcode, and permeated by the branches of the excretory canal- 

 system. Spicules of five kinds, viz. : — 1, the longest, consisting 

 of a delicate, smooth shaft, pointed internally, and terminated 

 externally by a trifid forked head (figs. 5, a, & 6, a) ; 2, shorter 

 than the last, but still long, straight, smooth, fusiform, acerate 

 (figs. 5, b, & 6, b) • 3, short, smooth, stout, curved, fusiform, 

 acerate (figs. 5, c, & 6, c) ; 4, minute, consisting of an extremely 

 delicate, flexible shaft, pointed inwardly and terminated at the 

 other end by a bifid or trifid, unequal-armed, forked head (figs. 

 6, d, & 7) ; 5, very minute, bihamate, contort, C- or S-like 

 (figs. 6, e, & 8). These spicules average respectively, as they 

 are described, 5-12ths, l-5th, l-18th, l-60th, and l-1800th of 

 an inch long. The two former, which are by far the longest, are 

 alone found in the conical expansion ; and the first, being 

 much longer than the second, extends beyond the latter, so that 

 the extreme border of the fringe is exclusively composed of 

 the trifid heads of the longest spicule (fig. 3, b, c, fig. 4). The 

 other three are confined to, and form the greater part of, the 

 structure of the head, mixed, also, with trifid and straight 

 acerate spicules of all sizes, like those of the conical expan- 

 sion, but much shorter. While the shafts of the trifid spicules 

 are hj far the longest, those of the acerate ones again are by far 

 the stoutest, being in the proportion of 1- to 3-1800ths of an 

 inch. Size of specimen : — height of summit of conical expan- 



